Horizontal wellbore orientation system

ABSTRACT

A horizontal wellbore orientation system and a method of making and using the same is provided. A horizontal wellbore orientation system of a hydrocarbon reservoir comprises at least one horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation. A method of constructing the system comprises determining the minimum and maximum horizontal stress of the formation based on fractal trends, and drilling at least one horizontal wellbore oriented substantially parallel to the minimum horizontal stress. A method of producing hydrocarbon using the system comprises drilling at least one horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation, injecting a fluid into the at least one horizontal well, and producing at least a portion of the reservoir hydrocarbon.

FIELD OF THE INVENTION

This invention is in the field of systems and methods for extracting hydrocarbon from fractured reservoirs, and more specifically, to recovery systems and methods using horizontal wells.

BACKGROUND

A large percentage of the world's oil and natural gas is confined to rock formations such as carbonates and granites. It is oftentimes difficult to extract these abundant and valuable commodities from the rock formations without natural or induced fractures in the rocks through which the fluids can permeate toward a production well. In areas of tectonic forces such as folds and faults, stress in a formation will cause natural fractures. In order to be of use in production, the fractures must connect a hydrocarbon reservoir to a wellbore. Induced fractures can be used to connect a well bore to any natural fractures that would otherwise not contribute to flow capacity. Induced fractures can be created by drilling stress or imposing hydraulic pressure.

Even with natural or induced fracturing within a rock formation, oftentimes the hydrocarbon to be extracted is highly viscous to the point that it will not flow naturally into a vertically- or horizontally-drilled production well. Furthermore, these reservoirs and their fracture trends are typically very complex, making hydrocarbon, such as heavy oil and bitumen, extraction a challenge. For these reasons, conventional extraction methods on these reservoirs yield low recovery rates.

An example of a naturally-fractured carbonate reservoir is the Grosmont Formation in the Western Canadian Sedimentary Basin. While bitumen is abundant in this formation, most of the recoverable oil in the reservoirs cannot be economically extracted with current extraction systems due to its complex fracture trends.

Generally speaking, in carbonate bitumen reservoirs, three different types of tectonic fractures have been noted: tension gashes, conjugate shears, and extensional fractures. The tectonic fractures, with the exception of the short tension gashes, are dominantly sub-vertical and form an orthogonal system with parallel and/or perpendicular orientations. These fractures are usually consistent with the fractal-scale regional pattern that is due to basement reactivation as documented in literature and as delineated with seismic ant-trackings.

There are several available options to aid the highly viscous hydrocarbons in permeating through these natural fractures to the production well, including the use of solvent-based and thermal recovery methods. These methods are designed to reduce the overall viscosity of the hydrocarbon to be extracted, allowing it to flow more easily through reservoir fractures and into the production well for extraction.

Cyclic steam stimulation or steam injection is one of the most promising thermal recovery methods for producing high viscosity hydrocarbons such as heavy oil and bitumen from naturally fractured formation reservoirs. This enhanced hydrocarbon recovery method requires a predetermined amount of steam to be injected into wells drilled into the hydrocarbon deposit. The hydrocarbon deposits could include, but are not limited to, oil sands, carbonate reservoirs, and/or shale reservoirs. The wells are then shut in to allow the steam and heat to soak into the reservoir surrounding the well. This assists the natural reservoir energy by thinning the hydrocarbon so that it will more easily move through the fractures in the formation and into the production wells. Once the formation has been adequately heated, the production wells are put back into production until the injected heat has mostly been dissipated with the produced fluids. This cycle is then repeated until the natural reservoir pressure has declined to a point that production is uneconomic, or until increased water production becomes a problem.

To further aid in production, wells can be drilled with a horizontal element to them (i.e. horizontal wells) rather than, or in addition to, the standard vertically-drilled wells. Drilling horizontal wells can expose more reservoir rock to a well bore than would otherwise be the case with a conventional vertical well. In areas where there is low matrix permeability in the horizontal plane, horizontal drilling can be preferred over vertical drilling by producing more oil than their vertical counterparts.

Despite a number of methods developed specifically for production from heavy oil reservoirs, including making use of natural and induced fractures in the rock formations, solvent and thermal recovery methods, and horizontal wells, and a combination of all of these, recovery still remains a challenge in rock formations due to the complexity and difficulty in extracting hydrocarbons such as heavy oil through a complex labyrinth of fractures. To date, attempts to produce hydrocarbons from many of these reservoirs have proven inefficient and uneconomical, and thus unfinished, leaving much of these resources untapped.

If systems and methods can be developed for more easily or effectively extracting hydrocarbon from these reservoirs, the recovery rates for known reservoirs could be significantly increased, which in turn, could have a significant impact on the world's oil and gas supplies.

SUMMARY OF THE INVENTION

It would be advantageous to have a horizontal wellbore orientation system in a fractured formation that allows for more effective hydrocarbon production.

In an aspect, a horizontal wellbore orientation system of a hydrocarbon reservoir comprises at least one substantially horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation.

In a further aspect, a method of constructing a horizontal wellbore orientation system in a formation comprises determining the minimum and maximum horizontal stress of the formation based on fractal trends, and drilling at least one horizontal wellbore oriented substantially parallel to the minimum horizontal stress.

In yet a further aspect, a method of hydrocarbon production from a hydrocarbon reservoir comprises drilling at least one horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation, injecting a fluid into the at least one horizontal well, and producing at least a portion of the hydrocarbon.

In exploiting the minimum and maximum horizontal stress regimes of a formation, horizontal wellbore orientations based on these regimes and oriented so as to lie substantially parallel to the minimum horizontal stress of the formation can allow for increased access to the hydrocarbon in the matrix, and thus increased resource production.

DESCRIPTION OF THE DRAWINGS

While the invention is claimed in the concluding portions hereof, preferred embodiments are provided in the accompanying detailed description which may be best understood in conjunction with the accompanying diagrams where like parts in each of the several diagrams are labeled with like numbers, and where:

FIG. 1 is a top plan schematic view of North-South, North-West, North-East, and East-West horizontal wellbore orientations in the Grosmont Formation;

FIG. 2 is a comparison plot showing incremental oil recovery for a horizontal well orientation parallel to the minimum horizontal stress and for a horizontal well orientation perpendicular to the minimum horizontal stress;

FIG. 3 is a well performance plot comparing the cumulative oil production of the wellbore orientations shown in FIG. 1 using equivalent steam injection volumes in the Grosmont Formation;

FIG. 4 is a well performance plot comparing the steam loss percentages of the 4 wellbore orientations shown in FIG. 1;

FIG. 5 is a flowchart of the steps performed in a method of constructing a horizontal wellbore orientation system; and

FIG. 6 is a flowchart of the steps performed in a method of hydrocarbon production using a horizontal wellbore orientation system.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

A horizontal wellbore orientation system and method of using the same is provided. This wellbore orientation system utilizes a wellbore orientation and configuration applicable for fractured hydrocarbon reservoirs utilizing any recovery method by fluid injection. It would be evident to a person of ordinary skill in the art that the term “hydrocarbon” as used herein can include many different forms of hydrocarbon in various densities, including, but not limited to, heavy hydrocarbons, heavy oil, extra heavy oil, and bitumen. In particular, the present system can be used for a thermal recovery method by means of steam injection to recover hydrocarbons such as heavy oil and bitumen from a naturally fractured carbonate formation.

FIG. 1 illustrates a horizontal wellbore orientation system 10 in a carbonate formation 20 in an embodiment of the present invention. The formation 20 shown is that of the Grosmont Formation in Alberta, Canada, though the principles of the present invention could be applied to any fractured reservoir or formation, whether the fractures occur naturally or are induced, and in any type of rock such as shale, carbonate or granite. In the present example, the system 10 is applied to the naturally fractured carbonate extra heavy oil and heavy oil reservoir of the Grosmont Formation.

A series of geological models were constructed using PETREL version 2012.5 application from Schlumberger based on the static data (logs, seismic, cores, etc.) from the Grosmont fractured carbonate formation. Subsequently, Discrete Fracture Network (DFN) was built using fracture network modeling in PETREL and up-scaled for the dual permeability flow simulation models. In this study Dual-Permeability module of STARS™ (advanced process and thermal reservoir simulator, version 2012) from Computer Modeling Group Ltd. was used to simulate and evaluate the performance.

The horizontal wellbore orientation system 10 and corresponding methods could be useful in any type of recovery method utilizing fluid injection, including thermal and solvent recovery methods. The system 10 and corresponding methods may be particularly useful in thermal recovery systems such as cyclic steam stimulation, which is a common recovery method that has been somewhat unsuccessfully piloted many times in the Grosmont Formation. This may be attributed, in part, to these pilot programs largely overlooking the importance of the stress patterns in the formation and failing to fully exploit the available fractures for effective wellbore permeation due to the complex fracture trends.

In areas of tectonic forces such as folds and faults, stress in a formation will cause natural fractures, with the entire formation exhibiting stress patterns indicating preferential directions showing up as overall minimum and maximum horizontal stress directions determined by the direction of regional stress. Induced fractures will typically also have a preferential direction, which is often parallel to the natural fractures. In fractured carbonate reservoirs, fractures parallel to the minimum horizontal stress will behave non-conductively; whereas fractures parallel to the maximum horizontal stress will behave conductively. Therefore, fractures parallel to the maximum horizontal stress, and particularly fracture clusters, will be a significant conduit for injected fluids.

The complex fracture trend of the Grosmont Formation 20 has open fractures 32 running North-East/South-West along the regional principal stress regime. The fractures 32 provide for a high permeability path for fluid movement in the low permeability rock formation 20. Fluid mobility and permeability are greater in the direction of maximum principal stress, shown in FIG. 1 in the direction of line A-A′, than in the direction of minimum principal stress, shown in FIG. 1 in the direction of line B-B′. Natural fractures 32 that trend in the direction of the maximum horizontal principal stress A-A′ are more permeable since they typically remain open, whereas fractures 32 that are perpendicular to the maximum horizontal principal stress B-B′ have generally lower permeability with less fracture propagation.

Current cyclic steam stimulation pilots and commercial applications in the Grosmont Formation use horizontal wells running in the North-South orientation only. On the contrary, in an aspect of the present invention, at least one horizontal wellbore 12 of the horizontal wellbore orientation system 10 is oriented perpendicular to this stress regime in order to expose the at least one horizontal well 12 to the maximum number of open fractures 32. This may increase conductivity of fluids, for example injected steam, into the formation 20.

The horizontal wellbore orientation system 10 is designed strategically based on the regional stress regime (the maximum A-A′ and minimum B-B′ horizontal stresses) in fractured reservoirs 20. The at least one horizontal wellbore 12 can be oriented substantially normal to the maximum horizontal stress A-A′ and substantially normal to the conductive fracture orientations to enhance hydrocarbon recovery from the fractured carbonate reservoir 20.

As mentioned previously, this system 10 can be applied to any rock formation having natural or induced fractures, and can be used with any recovery method utilizing horizontal wellbores, including thermal recovery methods and solvent recovery methods. In particular, the horizontal wellbores can be used in many types of thermal recovery schemes, including cyclic steam injection, steam flooding, water flooding, steam-assisted gravity drainage, and in situ combustion.

A series of numerical simulations were conducted on the various possible horizontal wellbore orientations of the Grosmont Formation 20: North-South, North-West, North-East, and East-West, with the simulations indicating that the highest bitumen recovery is achieved from the horizontal well orientation 12 that is parallel to the minimum horizontal stress B-B′.

FIG. 2 is a comparison plot of two different wellbore orientations in the Grosmont Formation, indicating that over 5% incremental oil recovery is obtained for the horizontal well orientation 12 parallel to the minimum horizontal stress B-B′ versus the well orientation North-East perpendicular to the direction of minimum horizontal stress B-B′.

FIG. 3 is a well performance plot comparing the cumulative oil production of the four wellbore orientations using the equivalent steam injection volumes in the Grosmont Formation 20. The four wellbore orientations compared are: North-South, North-West 12, North-East, and East-West. Given that the Grosmont Formation 20 has open fractures 32 running North-East/South-West along the regional principal stress regime A-A′, the horizontal wellbore 12 can be oriented substantially normal to these fractures 32; that is, the wellbores 12 can be oriented to run North-West/South-East to expose the wellbores 12 to the maximum number of open fractures 32 and thus result in an increase in output.

The overall result is a 30% potential increase in cumulative oil production of the North-West/South-East wellbores 12 as compared to the other wellbore orientation North-South, with equivalent steam injection volumes. The North-West/South-East orientation B-B′ shows a significant improvement over the conventional North-South wellbore orientation, which fails to take into consideration the regional fracture trends.

The increase in oil recovery for the horizontal well orientation 12 parallel to the minimum horizontal stress B-B′ could be attributed to increased accessibility to the hydrocarbon in the matrix. Specifically, the horizontal well orientation 12 parallel to the minimum horizontal stress B-B′ will maximize access to the maximum number of conductive flow paths of the fracture scheme.

FIG. 4 is a well performance plot comparing the steam loss percentages of the four wellbore orientations described above. This figure shows that the steam loss to the reservoir 20 in the North-West orientation B-B′ taking into account the regional fracture trend of the Grosmont Formation 20 is lower than the other three wellbore orientations North-South, North-East, and East-West. This suggests that more steam is retained to be used as useful heat in heating the resource, resulting in better reservoir performance through an improvement in the steam-oil ratio.

Referring to the flowchart in FIG. 5, in a method of constructing a horizontal wellbore orientation system in a formation in an aspect of the present invention, the minimum and maximum horizontal stresses of the formation can be determined based on fractal trends 50. The orientation of the stress state can be evaluated through a number of known methods, which may include the use of orthogonal calipers and other data from formation microscanning and formation microimaging, for example. In doing so, one might determine the optimum horizontal wellbore trajectory that will result in the intersection of the maximum number of fractures in the formation based on an orientation parallel to the minimum horizontal stress. A horizontal wellbore oriented along the optimum horizontal wellbore trajectory, which is substantially parallel to the minimum horizontal stress, can then be drilled 55.

Referring to the flowchart in FIG. 6, in a method of hydrocarbon production from a hydrocarbon reservoir in an aspect of the present invention, at least one horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation can be drilled at step 60. The at least one well can be drilled in addition to other horizontal wells and/or vertical wells. A fluid can be injected into the at least one horizontal well at step 62. This fluid may be any fluid that might permeate surrounding fractures and reduce the viscosity of hydrocarbons, and may include gases, solvents, steam, and heated water. As the hydrocarbon thins and permeates through the fractures, at least a portion of the hydrocarbon can be raised to the surface at step 64. The at least one horizontal well can be used as a conduit to raise at least a portion of the hydrocarbon in the reservoir to the surface at step 64, and/or the hydrocarbon could permeate into other drilled wells, which could either be vertical or horizontal wells, for production. These steps may be repeated cyclically, such as is done in cyclic steam stimulation recovery methods.

The foregoing is considered as illustrative only of the principles of the invention. Further, since numerous changes and modifications will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation shown and described, and accordingly, all such suitable changes or modifications in structure or operation which may be resorted to are intended to fall within the scope of the claimed invention. 

What is claimed is:
 1. A horizontal wellbore orientation system for a hydrocarbon reservoir comprising at least one substantially horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation.
 2. The system of claim 1 wherein the formation is fractured carbonate.
 3. The system of claim 1 wherein the formation is naturally fractured.
 4. The system of claim 1 wherein the formation comprises artificially induced fractures.
 5. A method of constructing a horizontal wellbore orientation system in a formation comprising: determining the minimum and maximum horizontal stress of the formation; and drilling at least one horizontal wellbore oriented substantially parallel to the minimum horizontal stress.
 6. The method of claim 5 wherein the step of determining the minimum and maximum horizontal stresses of the formation comprises the use of at least one of formation microscanning and formation microimaging.
 7. The method of claim 5 wherein the formation is fractured carbonate.
 8. The method of claim 5 wherein the formation is naturally fractured.
 9. The method of claim 5 further comprising the step of artificially inducing fractures in the formation prior to determining the minimum and maximum horizontal stresses of the formation.
 10. A method of hydrocarbon production from a reservoir comprising: drilling at least one horizontal well extending substantially parallel to the minimum horizontal stress of a surrounding formation; injecting a fluid into the at least one horizontal well; and producing at least a portion of the reservoir hydrocarbon.
 11. The method of claim 10 further comprising the step of using at least one of the at least one horizontal well as a conduit for producing at least a portion of the at least a portion of the reservoir hydrocarbon.
 12. The method of claim 10 further comprising the step of using at least one vertical well as a conduit for producing at least a portion of the at least a portion of the reservoir hydrocarbon.
 13. The method of claim 10 wherein the injected fluid is steam.
 14. The method of claim 10 further comprising a shut-in step wherein at least a portion of the injected fluid is allowed time to soak into the reservoir.
 15. The method of claim 14 wherein the steps of injecting a fluid into the at least one horizontal well, allowing at least a portion of the injected fluid time to soak into the reservoir, and producing at least a portion of the reservoir hydrocarbon are repeated in a cycle at least once.
 16. The method of claim 10 wherein the formation is fractured carbonate.
 17. The method of claim 10 wherein the formation is naturally fractured.
 18. The method of claim 10 wherein the formation comprises artificially induced fractures. 